A spring brake actuator is normally utilized for parking or emergency brake purposes.
A device of the kind described above--for obtaining a so called quick-release--is needed for the case that no fluid pressure is available for compressing the spring and thus for releasing the brakes and that the vehicle--preferably a rail vehicle--on which the actuator is mounted must be moved. Thus, the force transmitting path in the actuator from the spring to the member delivering its force from the actuator, in this case between the piston rod and the piston rod sleeve, must be broken by external, manual action but must be restored automatically at the return of brake fluid pressure for compressing the spring.
It is already known to employ a locking ring or spring ring for the general purpose set out above. In the design shown in the Swedish Patent Specification No. 7314474-3, especially FIGS. 4-6, the use of a spring ring is disclosed, although its purpose is different, namely to hold the actuator spring compressed in the absence of fluid pressure and automatically to release it at the return thereof.
However, in the present design the means for controlling the spring ring, based on the use of balls exerting an expanding force on the ring, are less developed and have certain disadvantages.